Field of the Invention
The invention relates to a method for providing a warning of radiation-dose-relevant space-weather events at cruising altitudes.
Description of the Relevant State of the Art
Due to the galactic cosmic radiation, exposure to radiation at the cruising altitudes of civil aviation (FL280-FL410) is increased by a factor of about 100 as compared to terrestrial exposures. The radiation field is heavily dependent on the local shielding effect of the terrestrial magnetic field, e.g. parameterized by the geometric latitude. This radiation field is further influenced by the variation of the interplanetary magnetic field due to the solar cycle. These different independent influences lead to a radiation field at cruising altitudes that is very complex in its composition and energy distribution.
Within the solar cycle, there exist, apart from the galactic cosmic radiation, also temporary radiation contributions by the solar cosmic radiation when, as a result of radiation bursts on the sun, i.e. so-called SPEs (abbreviation for solar particle events), particles are generated which are sufficiently energy-rich to penetrate the upper layers of the atmosphere. Due to secondary interaction of the primary radiation component with components of the atmosphere, such events also entail a distinct increase of corresponding count rates of ground-based instruments for measuring the intensity of cosmic radiation, i.e. so-called GLEs (ground level events and resp. ground level enhancements), and within the solar cycle they will occur with increased likelihood in the fading solar maximum.
The occurrence of radiation bursts on the sun that may lead to an additional radiation exposure at cruising altitudes, cannot be reliably predicted with the aid of the present state of the art, and such a prediction may even be principally impossible. The reason for this is, inter alia, that only the high-energy component (>500 MeV/n) of the particles emitted in such a solar radiation burst can enter the atmosphere deeply enough.
Presently, the Space Weather Prediction Center (SWPC) of the US National Oceanic and Atmospheric Administration (NOAA) will inform the public on the respective current space-weather situation and, via its homepage or an information service through email, will issue corresponding warnings (http://www.swpc.noaa.gov/). These warnings are based, as a physical evaluation quantity, on the flux of energy-rich particles at the position of the GOES-13 satellite (Geostationary Operational Environmental Satellite) of the NOAA. The classification of these warnings is performed by a scale (S-scale) whose index is given by the exponent of the flux of particles with energies above 10 MeV to the base 10. This classification is an evaluation of the radiation environment in near-earth orbits but is also extended to evaluations in the field of aviation. In the latter case, however, in consideration of the respective spectral index of the energy distribution of the incident particles, the major portion of the flux will normally be significantly below an energy threshold for dose-relevant contributions at cruising altitudes. In so far, in this scenario, false alarms are triggered which, in some airline companies, will result in unnecessary and cost-intensive measures.
In the absence of predictability of dose-relevant solar radiation contribution in aviation, such events can be detected only after the resultant increase of radiation intensity. Basically, this is possible by direct or indirect methods. On the one hand, the dose rate associated with the radiation exposure at cruising altitudes, i.e. both the energy dose rate dD/dt and the environment equivalent dose rate dH*(10)/dt can be measured directly in an aircraft with the aid of suitable dose meters. On the other hand, dose-relevant SPEs can also be monitored by a clear response of ground-based measurement instruments (e.g. neutron monitors). Also from a combination of the measurement data of various instruments, it is possible to estimate the corresponding data rates with the aid of radiation models, i.e. as is the case in direct measurement.
As already mentioned above, the Space Weather Prediction Center of the NOAA will inform the public situations of a space-weather event with increased proton influences which are measured at the position of the GOES-13 satellite. Classification of corresponding warnings will be performed by the S-scale whose index is given by the exponent of the flux of particles with energies above 10 MeV to the base 10. Since, however, due to the energy distribution in connection with the atmospheric shielding, the major part of the flux of incident parts normally will be significantly below an energy threshold for dose-relevant contributions at cruising altitudes, largely false alarms will be triggered in this scenario which, in some airline companies, will then entail unnecessary and cost-intensive measures. This has already had the consequence that these isolated warnings from the NOAA, based on unsuited physical parameters, have been generally ignored by some airline companies. Further, the S-scale used for classification of the space-weather events, will deliver only a global warning parameter and does not include a differentiation with respect to the really planned and respectively traveled route, e.g. under consideration of the corresponding local geomagnetic shielding.
Still, it has to be assumed that, irrespective of the above, most airline companies are interested in—or in need of—reliable, timely warnings of dose-relevant space-weather events.
It is an object of the invention to provide a method which is adapted to timely detect an additional, dose-relevant radiation component through a solar-particle event occurring at cruising altitudes and, with the aid of a model correspondingly adapted to the characteristics of the radiation burst, to make available, to users and the public, information on the radiation exposure at cruising altitudes both as a global and a regional warning. Thereby, e.g. airline companies will in case of a given event have the opportunity, by operational action, to carry out suitable radiation protection measures and effect a reduction of the dose according to §94 of the German Radiation Protection Ordinance (StrlSchV) under consideration of operational parameters.